Method for guiding vehicles automatically along a predetermined path

ABSTRACT

Low rate propagation of descrete phase points between two oppositely propagation and slightly detuned frequencies is used for motion control of vehicles along a prescribed path.

United States Patent Martin [451 Oct. 10,1972

[54] METHOD FOR GUIDING VEHICLES AUTOMATICALLY ALONG A PREDETERMINEDPATH Inventor:

Assignee:

Filed:

App]. No.:

Helmut Martin, Hannover, Germany Kabel-und MetallwerkeGutehoffnungshutte Aktiengesellschaft, Hannover, Germany Jan. 27, 1971Foreign Application Priority Data Feb. 13, 1970 Germany ..P 20 06 581.0

US. Cl. ..180/98, 340/32, 180/105 E Int. Cl. ..B60k 31/00 Field ofSearch ..180/98, 82, 105 E; 246/29,

References Cited UNITED STATES PATENTS l 2/ 1938 Southworth et a1..180/82 X 4/1943 Paulus et a1 ..246/167 R X 11/1951 Sunstein ..340/22 X12/ 1 954 Korman ..246/30 l/ l 962 Mountjoy ..180/98 X 7/1965 Wolfe..180/98 6/1967 French et a1. ..246/182 R Primary Examiner-Kenneth H.Betts AttorneySmyth, Roston & Pavitt ABSTRACT Low rate propagation ofdescrete phase points between two oppositely propagation and slightlydetuned frequencies is used for motion control of vehicles along aprescribed path.

9 Claims, 1 Drawing Figure The present invention relates to a method forguiding vehicles automatically along a predetermined path. Inparticular, the invention relates to a method for guiding motor vehiclesalong streets and highways by means of controlled motion. The inventionrequires employment of high frequency cable means, disposed along thepath and characterized by development of a partial external field.

The background of the invention is essentially based on the everincreasing traffic density and the corresponding increasing need forgreater safety. The object of the invention is to permit vehicles, forexample, automobiles to run on streets or highways without driverintervention. A method purporting to establish such a system mustfulfill the following requirements. First, the vehicle must remain on apredetermined track. Second, all vehicles that run on the same trackmust have the same speed or must follow a change in speed in aparticularly controlled manner so that, thirdly, all vehicles on thattrack maintain a safe distance from each other. There is no doubt thatsuch a system and the equipment for practicing such a method requires agreat deal of expenditure and investment for any extensive highway andsuperhighway systems to be so equipped. However, such investment cannotlonger be avoided in view of rapid deterioration of traffic safety onpresent day roads that do not provide for such automatic control.

It is an object of the invention to suggest a method and system forguiding vehicles along a track at very low expenditure, and whichpermits these requirements to be met. The method suggested in accordancewith the preferred embodiment of the present invention provides for thefollowing steps. As stated, a high frequency cable that develops apartial external field along its extension is to be provided along thevehicles path, road or track. It is convenient but not essential inprinciple to provide such cable in the center of any lane if the methodis used for control of automobiles. Alternatively, the cable may beinstalled next to the road or inbetwe'en two lanes for servicing both ofthem. For a given highway or street section, that cable has two terminalpoints which are to be connected to two transmitters feeding highfrequency energy into that cable for propagation therein in oppositedirections. However, the frequencies differ in that they are bothapproximately subharmonics of a particular control frequency, i.e., thetwo transmitted frequencies are to have approximately a common harmonic.The particular control frequency or harmonic has been derived from, oris developed by, a common frequency standard. The term approximate is tomean that at least one of the transmitted frequencies differs from atrue subharmonic of that particular frequency in a controlled manner.

The vehicles are equipped with receivers tuned to the transmittedfrequencies. Comparable harmonics are extracted from the two receivedsignals, and circuitry connected to the receivers compare the phase ofthe two separately developed harmonics. The phase comparison is used totrack discrete phase points along the cable corresponding topredetermined phase relation between the two harmonics. Since at leastone of the two transmitter frequencies deviates from being a truesubharmonic of the control frequency, the discrete phase pointspropagate along the cable at a speed represented by that deviation.Thus, tracking of these moving phase points requires the vehicle to movealong the road at that speed which is the desired and controlled speedfor all vehicles along the cable. The

receivers and connected circuitry in the vehicles are adjusted toprovide a command for controlling vehicle motion to maintain position inrelation to a discrete point as propagating in particular directionalong the cable.

The discrete points are preferably selected by phase difference of or270 (i.e., or 1r/2) of the control frequency because phase detectors areusually constructed to provide zero d-c output forsuch a phase relation.If the two transmitter frequencies are precisely subharmonics of theparticular frequency, the phase of the two signals of the particularcontrol frequency, as extracted from the two received subharmonics isconstant, i.e., such a discrete phase point is stationary. As thefrequency of at least one transmitter is varied from that relation, thephase points along the cable are set into motion. The speed isessentially freely selectable corresponding to adjustment of one (or inboth) transmitters.

While the specification concludes with claims particularly pointing outand distinctly claiming the subject matter which is regarded as theinvention, it is believed that the invention, the objects and featuresof the invention and further objects, features and advantages thereofwill be better understood from the following description taken inconnection with the accompanying drawings in which:

The FIGURE illustrates schematically a system for practicing the methodof the invention.

Take any street, highway, superhighway etc., a high frequency cable 10is layed on that road, for example, in the center of or along a lane.The disposition of the cable is-illustrated schematically only, but anoverhead installation is likewise possible. The cable may be a coaxialcable with a core and a shield surrounding the core but having anaxially extending slit to develop a partial field 11 external to theshield and outer conductor of the cable.

The cable extends over a particular stretch of the road and has twoends; there are provided two transmitters, l2 and 13, feeding highfrequency energy into the cable from opposite ends to propagate throughthe cable in opposite directions. Transmitter 12 on one end of the cableprovides, for example, high frequency energy at a frequency f1;transmitter 13 on the other end of the transmission line provides highfrequency energy at a frequency f2. In the illustrated example it isassumed that frequency fl is precisely the fifth subharmonic of a signalfrequency f0, i.e., fl f0/5. The frequency f2 is merely approximatelythe sixth subharmonic of that frequency fo, i.e., f2 fol6 Af. Frequencyfo is the critical control frequency of the system.

As far as the transmission system is concerned, it is necessary that thetwo transmitters operate in predetermined synchronism. Particularly,the'relative values of the frequencies are critical, so that it isnecessary to make sure that operation of both transmitters relatesparticularly to. the same control frequency f0. Therefore, there isprovided a frequency standard or master oscillator 14 which providesthat control frequency fo. Master oscillator 14 can be'located anywhere,but conveniently it is disposed at one of the locations for thetransmitters. In the present example, the oscillator 14 is presumed tobe located at transmitter 12 and separate transmission means may belocated at transmitter .12 and separate transmission means may beprovided to transmit that frequency fo to the other transmitter 13 forutilization therein. The frequency fo may be transmitted in form ofcarrier modulated Rf transmission or via cable etc. Conceivably however,transmitter station 13 receives signal fo/S, extracts therefrom'fo andconstructsther'efrom signal fo/ 6.

Speaking generally, the transmitters use control frequency f0, and theyderive therefrom respective two subharmonic, namely, fo/S in transmitter12, and fo/6 in transmitter 13. The signal, as transmitted bytransmitter 13, is modulated additionally as will be explained shortly.To develop .the description of the system, it may be assumed presentlythat Af= 0. Signals of the two subharmonics of f are fed into the cablesystem, so that fo can be extracted from either transmitted signal alongthe road. It is required that the propagation speed for the twofrequencies is uniform along the high frequency cable (subject tointentional variation as will be explained below). In view of the factthat, generally, two waves of the same frequency and propagating inopposite direction, produce a standing wave when combined, two suchwaves without combining produce time independent constant phase pointsbetween the two waves, corresponding to nodes of a standing wave. Theseconstant phase points are preferably selected as discrete points andthey are stationary along the cable (at a distance spaced apart by ahalf a wavelength of the signal frequency f0).

As stated, any vehicle 20 travelling on that road includes tworeceivers, such as 21 and 22, and is in that respect similar equipped asan aircraft for the so-called Decca method in air navigation. The tworeceivers are individuallytuned to the two different frequencies f0/5and fo/6, respectively, and receive them separately accordingly. Thesetwo signals, as separately received, are individually transformed indetector circuits 23 and 24 respectively, whereby circuit 23 providesthe fifth harmonic of the signal it receives (which is f0) while circuit24 provides the sixth harmonic of the signal it receives, which is alsof0, as long as both transmitter frequencies are precisely subharmonicsof that frequency.

The two thusly gained signals of the frequency f0 are compared as totheir phase in a phase detector 25,.constructed, for example, to providezero output for 90, or for a 90 phase difference, depending upon itsconstruction. Positive or negative d-c outputs of the phase detector 25represent a displacement of the vehicle in one or the other directionfrom such a phase point. That phase detector output, thus, representsactual physical alignment or misalignment of the vehicle with adiscrete, constant phase point as defined. Conversely, one can say thatsuch a phase point is defined where the particular phase detectorproduces zero output.

The receiver equipment on the vehicle generally is coupled to a followercontrol system in that the output of detector 25 provides a commandsignal for control of the gasoline feed to the carburetor in the vehicle(and, possibly, also to the brake system).

Without further measures, the vehicle would be moved into alignment witha stationarydiscrete point and stay there. This situation may well occurif for reasons of an emergency the entire traffic on that road is to behalted.

After having described the stationary case, I proceed to the descriptionof the speed control case. For this, the discrete points are set intomotion, and the circuit in a vehicle operates to control speed anddisposition of the vehicle to be equal to the speed and location of theclosest discrete point as propagating along the cable. The phasecomparison and resulting output causes the vehicle to track thepropagating discrete point.

The speed of the discrete points are determined in that the frequency ofone transmitter, e.g., transmitter 13, is changed by an incrementalvalue Af, i.e., f2 =f0/6 Af, with Af 0. The Af-generator is denoted withreference numeral 15 in the drawing. The sixth harmonic of the signalfrequency as now transmitted by transmitter 13 is no longer preciselyf0, but the detuned signal frequency f2 is still within the band widthof receiver 24. Therefore, the discrete point, defined as a particularphase (i of the fifth and sixth harmonic of the two transmitterfrequencies as received will no longer be stationary but propagatesalong the cable. For Af 0, the discrete phase points in question movefrom transmitter 12 to transmitter 13, for Af 0 the direction is theopposite one.

The velocity Vk of the discrete phase points is given by the relationwherein V0 is the propagation speed for the signal in and along cable10. The phase detector 25 in each vehi-. cle tracks the closest discretephase point and, thus, moves at that speed Vk.

It is, of course, possible to decrease the output frequency oftransmitter 12 by the same amount or to detune both transmitterfrequencies oppositely, each by half of that amount Af. However, thatlatter method is mentioned here only for reasons of completion, as it isobviously simpler to change but one of the two transmitter frequencies,particularly in case controlled variation of the speed is desired Also,in that case, a constant frequency output of the respective othertransmitter (in the example, transmitter 12) may be used as a reference.For example, at transmitter station 13, the signal fo/5 is received,transformed to reproduce f0, and f0/6 is then derived therefrom asstated above.

The frequency changes as imparted upon one of the transmitters are verysmall because Vk/Vo is in the order of 10 to 10". The generator 15 forAf may, for example, be a rotating coil. Thus, a magnetic high frequencyrotating field is produced, having frequency fo/6. A coil is providedtransverse to that field and rotates mechanically rather slowly. Avoltage is induced in the rotating coiland the frequency of that voltageis the sum of the field frequency and of the mechanical rotationalfrequency. That sum is used for control of the output stage of thatparticular transmitter. Upon control of the mechanical rotation, theincremental frequency Af is controlled so as to control and possiblyvary the desired vehicle speed Vk. such control in time may be desirablefor adaptation of the system to different weather and road conditions,traffic density and, as stated above, emergency situations.

In order to avoid collision accidents, it is necessary that two vehiclestravelling along the same track keep a minimum safe distance from eachother. Two vehicles that have their controls operate to track the samediscrete point will clearly collide. A minimum distance between twovehicles is, thus, the distance between two discrete phase points, asthey travel along the h.f. cable. That distance depends upon thefrequency f0. However, for reasons of irregular vehicle motion an unuseddiscrete point should remain between two vehicles. Accordingly, thecontrol frequency fo of the system is selected in accordance with theequation f0 Vo/4s, wherein s is the minimum distance from vehicle tovehicle and V0 is the propagation speed for the h.f. signals in cable10.

The basic principles mentioned above will establish a I system in whichthese discrete points propagate at con stant speed along the h.f. cableas the control mechanism in each vehicle will tend to control vehiclepropagation accordingly. It has to be observed, however, that the speedalong the road should not necessarily be a uniform one. Sharp curves andhills, transition lanes leading from one highway to another requireusually a lower speed. Also, the entrance or on-ramp of such acontrolled highway is preferably provided for relative slow speed,gradually changing into higher speed. In accordance with another featureof the invention, it is, therefore, suggested to lower the propagationspeed of high frequency energy locally in cable 10.

Generally speaking, the propagation speed of the h.f.

energy in cable is inversely proportional to the square root of theproduct of dielectric constant and permeability of the propagationmedium. To lower the propagation speed that product has to be increased,for example, by including ferromagnetic material in the dieelectricmaterial that is part of the cable. This,'however, is just one of thebasically known methods to increase the product of transmission lineinductivity and transmission line capacity so that the propagation speedof high frequency energy, and, therefore, the speed of the discretephase points, as compared with the speed along other portions of thecable, is reduced. It follows that the speed of the vehicle iscontrolled to a lower value along such portions of the cable wherebyalso automatically the distance s between the vehicles is lowered uponreduction of velocity, (s Vo/4f0) as the distance between thepropagating discrete phase points is reduced along those cable portionsac cordingly.

The vehicles are maintained on the respective track by operation ofmeans as they are known per se. This is mentioned here only todemonstrate that the inventive method and system meets all three of therequirements mentioned in the introduction. Two pickup coils areprovided on each vehicle, and they are connected to circuitry that isresponsive to the strength of the high frequency field as pick-up fromthe high frequency cable. The signal amplitudes or envelopes arecompared and, e.g., their difference or ratio is used as command inputfor an automatic steering mechanism of the vehicle. For this, it is, ofcourse, best to provide the cable on and along the center line of theparticular lane, and the controlled steering mechanism of the vehiclemaintains the vehicle centrally above that cable. Of course, the cablemay be provided as an overhead line, and the vehicle is steered toremain centrally under that line. In case the cable is disposedalongside the road (which may be more economical) the steering controlhas to respond to a particular ratio (other than unity) for the pickedup signals. The particular steering control circuit is preferably tunedto one of the two frequencies as they are readily available, but it isbasically possible to feed a third frequency into the cable for steeringcontrol. Employment of additional frequencies for steering is ofadvantage for other reasons, namely in case of branching, so that thecontinuing path and the branch path are identified by different steeringcontrol frequencies. Adjusting of the receiver for steering control toone particular frequency safeguards that the vehicle remains on thedesired track and enters (or avoids) a highway branch. One can thinkhere of a signal representation of highways having different numbers, asis conventional. Sometimes different highways have a common section, butsplit at either end of such section. As can readily be seen by providingdifferent steering frequencies corresponding to different numbers ofhighways, the vehicle will be maintained on the right track.

As stated, the inventive method lends itself to utilization of one ofthe signals for steering. However, also selective steering and branchingcan be provided for directly. For practicing this particular aspect ofthe inventive method, it can be assumed, for example, that the signal offrequency fo/S is transmitted from starting points of one or twohighways. It is assumed in both cases that there is a common sectionfrom which the two highways branch toward different destination points.The transmitter at the destination end of one of the two branchinghighways feeds f0/6 Af, and the transmitter at the end of the otherhighway feeds frequency f0/4 Af into the cable. Production of theincremental frequency Af at the different locations must besynchronized, and the relative phases of the several signals must beadjusted, so that the phase points of the fo/5 fo/6 Af comparison and ofthe fa/5 fo/ 4 Af comparison, coincide at least ap-' proximately.

The common portion of the cable receives all frequencies, but a vehicletuned to a particular pair of frequencies is automatically guided in thecorrect branch. On the other hand, the relation of the frequencies, asstated, makes it readily possible that the discrete points, includingthe points in the common section where the vehicles with differentdestinations may propagate and intermingle, still remain at the .properdistance between the vehicles, particularly, if the vehicles have atleast twice the minimum distance ahead of the point of merging traffic.

A particular point that has to be considered is, that, depending uponselection of the type of high frequency cable, but to some extent in allcases, the signal frequencies are attenuated as they propogate along thecable. It is, therefore, necessary to make sure that a minimum fieldstrength is available along the cable for pick-up, and this, in turn,requires placement of amplifiers within the transmission line. The twodifferent frequencies require amplification in different directions sothat it is necessary to separate the two frequencies, as originating inthe two different transmitters.

The amplifiers must be operated in phase synchronism as to respectiveinput and output, so that there is no phase jump; i.e., the discretepoints must travel through the amplifiers without change in speed.

The invention is not limited to the embodimentsdescribed above but allchanges and modifications thereof not constituting departures from thespirit and scope of the invention are intended to be included.

I claim:

1. A method of controlling the motion of vehicles along a prescribedpath comprising the steps of:

providing a high frequency cable for developing partial external fieldalong said path to radiate high frequency energy along that path;

feeding h.f. energy of a first frequency into the cable,

from one end thereof and to propagate therein in a direction away fromthe feed-in point; feeding h.f. energy of a second frequency into thecable from the opposite end to propagate therein in the oppositedirection, the first and second frequencies both being approximatelysubharmonies of a particular frequency, the total deviation of both ofthe first and second frequencies from respectively being a truesubharmonic of the particular frequency representing a phase pointvelocity along the cable; detecting, in. a vehicle in the vicinity ofthe cable,

signals of the first and second frequencies;

detecting, in the vehicle, particular harmonics in each of the detectedsignals and comparing the phase between the separately detectedharmonics; and

the vehicle in response to the controlling motion of phase comparison.

2. A method as in claim 1, wherein the motion of the vehicle iscontrolled to maintain a constant phase betweenthe harmonic as derivedfrom the signal of the first .frequency and the harmonic as derived fromthe signal having the second frequency.

3. A method as in claim 2, wherein the. motion is controlled to maintaina phase difference.

4. A method as in claim 2, wherein themotion is controlled to maintain a90 phase difference.

5. The method as in claim 1, wherein the first frequency is a truesubharmonic of the particular frequency, the second frequency is acomposite frequency that includes another true harmonic of theparticular frequency and an incremental component representing the phasepoint velocity.

6. The method as in claim 5, wherein the incremental component is equalto twice the second frequency multiplied by the ratio of phase pointvelocity and wave propagation velocity in the cable. 7

7. The method as in claim 5, providing the second frequency by firstproviding an h.f. rotating field having frequency of the other trueharmonic, and providing a rotating coil in the field, to derivetherefrom the composite frequency as second frequency to be transmittedthr h the cable.

8 'he method as in claim 1, wherein the particular frequency is selectedto be equal to the propagation speed of high frequency energy within thecable divided by four times the distance to be maintained between twosucceeding vehicles.

9. The method as in claim 1, comprising the step of selecting arelatively reduced wave propagation velocity in portions of the highfrequency cable as compared with the wave propagation velocity in otherportions of the cable, in accordance with a reduced desired phasevelocity in the vicinity of the cable.

t i =8 t

1. A method of controlling the motion of vehicles along a prescribedpath comprising the steps of: providing a high frequency cable fordeveloping partial external field along said path to radiate highfrequency energy along that path; feeding h.f. energy of a firstfrequency into the cable, from one end thereof and to propagate thereinin a direction away from the feed-in point; feeding h.f. energy of asecond frequency into the cable from the opposite end to propagatetherein in the opposite direction, the first and second frequencies bothbeing approximately subharmonics of a particular frequency, the totaldeviation of both of the first and second frequencies from respectivelybeing a true subharmonic of the particular frequency representing aphase point velocity along the cable; detecting, in a vehicle in thevicinity of the cable, signals of the first and second frequencies;detecting, in the vehicle, particular harmonics in each of the detectedsignals and comparing the phase between the separately detectedharmonics; and controlling motion of the vehicle in response to thephase comparison.
 2. A method as in claim 1, wherein the motion of thevehicle is controlled to maintain a constant phase between the harmonicas derived from the signal of the first frequency and the harmonic asderived from the signal having the second frequency.
 3. A method as inclaim 2, wherein the motion is controlled to maintain a + 90* phasedifference.
 4. A method as in claim 2, wherein the motion is controlledto maintain a - 90* phase difference.
 5. The method as in claim 1,wherein the first frequency is a true subharmonic of the particularfrequency, the second frequency is a composite frequency that includesanother true harmonic of the particular frequency and an incrementalcomponent representing the phase point velocity.
 6. The method as inclaim 5, wherein the incremental component is equal to twice the secondfrequency multiplied by the ratio of phase point velocity and wavepropagation velocity in the cable.
 7. The method as in claim 5,providing the second frequency by first providing an h.f. rotating fieldhaving frequency of the other true harmonic, and providing a rotatingcoil in the field, to derive therefrom the composite frequency as secondfrequency to be transmitted through the cable.
 8. The method as in claim1, wherein the particular frequency is selected to be equal to thepropagation speed of high frequency energy within the cable divided byfour times the distance to be maintained between two succeedingvehicles.
 9. The method as in claim 1, comprising the step of selectinga relatively reduced wave propagation velocity in portions of the highfrequency cable as compared with the wave propagation velocity in otherportions of the cable, in accordance with a reduced desired phasevelocity in the vicinity of the cable.